1. Field of the Invention
The present invention relates to a photosensitive material advantageously employable for preparing a color proof or a display sheet.
2. Description of Prior Art
There are heretofore known various image transfer processes comprising a step of imagewise exposing a photosensitive transfer material comprising an undercoat layer of an organic polymer, a coloring material layer and a photosensitive layer provided on a temporary support to light; a step of developing it to form a color image on the undercoat layer; and a step of transferring the image to a permanent support using an adhesive (see, Japan Patent Publication Nos. 46(1971)-15326 and 49(1974)-441). These processes have advantages in that they can be used for preparing color proof in various procedures such as those of an overlay type and a surprint type. However, these processes have disadvantages in that an adhesive must be used in every transferring procedure and hence the processes are complicated and in that there is difficulty in keeping the accuracy of registration in transferring each color.
To eliminate the complicated procedures of the process, there have been proposed methods wherein after the formation of an image, the image is transferred to a permanent support under the application of heat and pressure (see, Japanese Patent Provisional Publication No. 47(1972)-41830, No. 48(1973)-9337 and No. 51(1976)-5101). Particularly, Japanese Patent Provisional Publication No. 51(1976)-5101 describes that an adhesive hot-melt polymer layer is provided on a permanent support and Japanese Patent Provisional Publication No. 47(1972)-41830 describes that an image is transferred directly to a permanent support such as an art paper sheet or a coated paper sheet.
However, these processes have still various disadvantage in that the final image is transferred to a permanent support in such a manner that the right and the left are reversed against the original image and in that when a hot-melt polymer is used as an adhesive, the melting point thereof is usually high and hence the transferring temperature must be high so that the dimensional stability of the support is lowered by the action of heat and the deviation of colors from one another in the registration procedure is caused when each color is transferred. When a hot-melt polymer having a low melting point is used as an adhesive, there are caused problems that after the formation of an image, sticking is observed, or the surface thereof is liable to be damaged.
As a method for eliminating the above-described disadvantages, there is proposed in Japanese Patent Provisional Publication No. 59(1984)-97140 a process wherein an image is transferred to a temporary image-receiving sheet before the image is transferred to a permanent support. This process includes steps of: preparing a temporary image-receiving sheet provided with an image receiving layer of a photopolymerizable material on a support; transferring an image of each color is transferred to the temporary image-receiving sheet; retransferring said image to a permanent support; and exposing a whole surface of it to light to cure the transferred photopolymerizable image receiving layer.
The above-described image transferring process using the temporary image-receiving sheet (hereinafter referred to simply as image-receiving sheet) is very effective in eliminating the aforementioned problems. In more detail, there are given the following advantages. An erect image of the masked original can be obtained on the permanent support. Since an ethylenically unsaturated polyfunctional monomer serving as a photopolymerizable substance is incorporated in the photopolymerizable image receiving layer of the image-receiving sheet, the photopolymerizable image-receiving sheet itself is soft, the transferring can be carried out at a low temperature, and after transferring, it can be exposed to light to cure. Thus, there are given advantages that after the transfer of the image, sticking is not observed and the final image has high resistance to damage.
As the photosensitive transfer material used in the image transferring method, there is generally used a photosensitive material comprising an undercoat layer of an organic polymer, and a coloring material-containing photosensitive layer (or a laminate composed of a coloring material layer and a photosensitive layer) in order in the form of a laminate. The undercoat layer not only functions as a peel layer but also gives an improvement of an image transferring property.
The undercoat layer is required to have the following properties: 1) showing an appropriate bonding strength to a temporary support and capable of being peeled from it; 2) showing nontackiness at room temperature and showing tackiness or fusibility depending on heating to keep transferring property; and 3) showing a barrier property that a coloring material contained in the a coloring material-containing photosensitive layer or a laminate of a coloring material layer and a photosensitive layer does not enter the undercoat layer when such layers are coated.
Lack of the barrier property causes the coloring material to enter the undercoat layer. If the coloring material is entered into the undercoat layer, the coloring material generates color fogging and hence brings about deterioration of quality of a resultant image. Further, in the case where a naphthoquinone diazide compound (the foot of the absorption spectrum of said compounds extends to reach the visible light region) is used as a photosensitive materials, color fogging is caused and the quality of the image lowers when the compounds are introduced into the undercoat layer.
In the formation of the coloring material-containing photosensitive layer or the coloring material layer as mentioned in 3) above, there is often used a coating solution containing an alcohol such as methanol, ethanol or propanol as a solvent. Hence, the undercoat layer is required to show barrier property against the solvent.
For example, Japanese Patent Provisional Publication No. 63(1988)-2037 discloses a photosensitive material using alcohol-soluble polymer (e.g., polyamide) as material of an undercoat layer. Accordingly, when the photosensitive material is used, occurrence of the color fogging and lowering of the quality of a image are not satisfactorily prevented owing to alcohol-soluble property of the polymer of the undercoat layer. Further, in the case that transferring is conducted using the photosensitive material particularly under the conditions of low temperature and low humidity, small bubbles are apt to enter into the formed image (e.g., a barrier layer or coloring material-containing photosensitive layer) so that quality of the final image often lowers.
To solve the above-problems, Japanese Patent Provisional Publication No. 63(1988)-2039 discloses a photosensitive material having a peel layer of an alcohol-soluble polymer, a barrier layer of an alcohol-insoluble polymer, and a coloring material-containing photosensitive layer (or a laminate composed of a coloring material layer and a photosensitive layer) in order in the form of a laminate. In the above photosensitive material, the peel layer and the barrier layer are used instead of the undercoat layer. Using the photosensitive material, the color fogging is not caused and the quality of an image does not lower under an ordinary environment.
However, in the case that transferring is conducted using the photosensitive material particularly under the conditions of low temperature and low humidity, small bubbles are apt to enter into the formed image (e.g., a barrier layer or coloring material-containing photosensitive layer) so that quality of the final image often lowers.
The inventors studied to solve the above problem and has discovered the following:
In the case that a polymer having high glass transition temperature is used as a polymer material of the peel layer, incorporation of bubbles into an image is decreased but registration in the transferring procedure becomes difficult. Further, in the case that a polymer having low glass transition temperature or a polymer containing plasticizer is used as a polymer material of the barrier layer, extent of mixing of the barrier layer with other layer or extent of color fogging increases, or uniformity of a surface of the barrier layer lowers. On the other hand, increase of thicknesses of these layers decreases incorporation of bubbles. However, increase of light scattering by the thick layers deteriorates quality of the final image. Thus, there is desired a photosensitive material in which a resultant image have a high quality, transferring property is excellent even under the conditions of low temperature and low humidity and color fogging is little.